Sub-surface wells typically include a shaft that is lined with piping known as “casing.” Into the casing is inserted piping known as “tubing.” When a well is drilled, it is not yet determined what kind of production the well will give up or produce. Most wells will produce fluid and gas naturally through the tubing without the assistance of a mechanical pumping unit during the beginning phase of the life of the well. In this first phase of production, many wells produce high volumes of gas with fluid, the fluid typically consisting of oil, water, and solids entrained therein. The formation geology where the well production is in this first phase has substantial natural pressure built up over time. This natural pressure allows the production fluid to be pumped or produced to the surface naturally, without the assistance of a mechanical pumping unit. Eventually, the bottom-hole pressure of the well formation subsides to a lower pressure. When that occurs, the fluid that was once being produced by natural pressure can no longer be forced to the surface through the tubing. When this takes place, the weight of the well fluid being produced will prevent the gas from being produced, due to the hydrostatic pressure of the fluid being held in the tubing column. The pressure of this fluid on the well's geologic formation stops most of the remaining gas from entering the wellbore. When the well reaches this point in production, an artificial method is required in order to pump the fluid, and the well then enters the second phase of production.
Oil well pumping systems are well known in the art. Such systems are used to mechanically remove oil or other fluid from beneath the earth's surface, particularly when the natural pressure in an oil well has diminished. Generally, an oil well pumping system begins with an above-ground pumping unit, which may commonly be referred to as a “pumpjack,” “nodding donkey,” “horsehead pump,” “beam pump,” “sucker rod pump,” and the like. The pumping unit creates a reciprocating (up and down) pumping action that moves the oil (or other substance being pumped) out of the ground and into a flow line, from which the oil is then taken to a storage tank or other such structure.
Below the ground, a shaft is lined with casing. Into the casing is inserted tubing. Inside the tubing is inserted a string of sucker rods, which ultimately is indirectly coupled at its north end to the above-ground pumping unit. The string of sucker rods is ultimately indirectly coupled at its south end to a subsurface or “down-hole” pump that is located at or near the fluid in the oil well. The subsurface pump has a number of basic components, including a barrel and a plunger. The plunger operates within the barrel, and the barrel, in turn, is positioned within the tubing. It is common for the barrel to include a standing valve and the plunger to include a traveling valve. The standing valve has a ball therein, the purpose of which is to regulate the passage of production fluid—which includes oil mixed with water and gas—from down-hole into the pump, allowing the pumped matter to be moved northward out of the system and into the flow line, while preventing the pumped matter from dropping back southward into the hole. Oil is permitted to pass through the standing valve and into the pump by the movement of the ball off its seat, and oil is prevented from dropping back into the hole by the seating of the ball. North of the standing valve, coupled to the sucker rods, is the traveling valve. The traveling valve regulates the passage of oil from within the pump northward in the direction of the flow line, while preventing the pumped oil from dropping back southward, in the direction of the standing valve and hole.
Actual movement of the pumped substance through the system will now be discussed. Oil is pumped from a hole through a series of downstrokes and upstrokes of the pump, which motion is imparted by the above-ground pumping unit. During the upstroke, formation pressure causes the ball in the standing valve to move upward, allowing the oil to pass through the standing valve and into the barrel of the oil pump. This oil will be held in place between the standing valve and the traveling valve. In the traveling valve, the ball is located in the seated position, held there by the pressure from the oil that has been previously pumped.
On the downstroke, the ball in the traveling valve unseats, permitting the oil that has passed through the standing valve to pass therethrough. Also during the downstroke, the ball in the standing valve seats, preventing pumped oil from moving back down into the hole. The process repeats itself again and again, with oil essentially being moved in stages from the hole, to above the standing valve and in the oil pump, to above the traveling valve and out of the oil pump. As the oil pump fills, the oil passes through the pump and into the tubing. As the tubing is filled, the oil passes into the flow line, and is then taken to the storage tank or other such structure.
There are a number of problems that are regularly encountered during fluid production operations. Fluid that is produced from the ground is generally impure, and includes solid impurities such as sand, pebbles, limestone, grit, iron sulfide, and other sediment and debris. Certain kinds of sub-surface fluids, such as heavy crude, tend to contain a relatively large amount of solids. During the first phase of well production, eventually, the natural pressure in the well diminishes. As this occurs, solids settle back into the wellbore, gas is not permitted to escape upward, and the fluid begins to accumulate, thereby reducing the natural production of fluid and gas.
With respect to fluid production through mechanical pumping systems, typically, when such pumping operations have stopped, the solid impurities entrained in the fluid being pumped begin to settle, and they settle onto the pumping components. For example, the tubing joints may become completely filled with solid impurities, leading to damage and eventual pump failure. In this regard, in typical pumping systems, oftentimes the bottom first through fourth tubing joints completely fill with solid impurities, creating a plug. Even if pump failure does not result, this plug will eventually prevent the pumped fluid from passing. The plug can also lead to rod failure, due to compression loading.
The present invention addresses these problems encountered in prior art pumping systems and provides other, related advantages.